In the manufacturing of integrated circuits, the control of the dimensions of the devices is important for improving the performance of the integrated circuit devices. The control of the dimensions of the devices, however, is difficult. The reason is that the widths of the resulting feature may deviate widely due to the effect of many factors, including the characteristics of the features that formed before the lithography process. Therefore, with the many factors in the preceding processes involved, it is difficult to adjust a subsequent lithography process to cancel the adverse effect of the preceding process steps.
An example of the lithography process is the etching of a gate electrode layer to form gate electrodes. The widths of the gate electrodes are important for the performance of the respective transistors. The widths of the gate electrodes thus need to be controlled carefully. The lithography process for forming the gate electrodes, however, may be affected by the factors include, but not limited to, the height difference between the top surface of the active regions (on which the gate electrodes are to be formed) and the top surface of the adjacent shallow trench isolation regions, the pre-doping concentration of the gate electrodes, the thickness of the hard mask that is used for etching the gate electrode, etc.